1. Field of the Invention
This invention generally relates to an isocyanate-terminated polysiloxane material and more particularly to an isocyanate-terminated polysiloxane material for use as a curing agent, hardener or co-reactant in coatings.
2. Description of Related Art
A typical two-component polyurethane system consists of an isocyanate-reactive polymer and an isocyanate or polyisocyanate. “Two-component” (also known as 2K) simply describes a paint system that is composed of a base paint and a hardener both of which are packaged separately. Before application of the paint, the base paint is mixed with the hardener in a predetermined ratio to initiate a chemical reaction. This paint mixture remains usable for a period of time known as pot life which varies depending on the formulation. The chemical reaction proceeds until gelation finally occurs. A two-component polyurethane, for example, may be composed of a polyol as the base and a polyisocyanate as the hardener.
Polysiloxanes have found their way into many areas including medical and non-medical fields. Medical applications of polysiloxanes include prostheses, artificial organs, facial reconstruction, catheters, artificial skin, contact lenses, and drug delivery systems. Non-medical applications include high-performance elastomers, membranes, electrical insulators, water repellants, anti-foaming agents, mold release agents, adhesives and protective coatings, release control agents for agricultural chemicals, and hydraulic, heat-transfer, and dielectric fluids. The use of polysiloxanes in coatings is increasing due to their ability to impart desirable characteristics such as improved chemical resistance, improved weatherability, improved flexibility, increased hydrophobicity and greater permeability to gases (while remaining impermeable to particles) compared to other polymers. In addition, polysiloxanes have lower surface energy (i.e. lower surface tension) and can therefore, provide higher slip properties and greater wettability which is why silicones have been primarily used as coating additives. This can bring lower viscosities in coatings and reduce the need for solvents which will lower the volatile organic content (VOC) of the coating system. However, alone polysiloxanes do not produce a desirable coating as they are very brittle.